In recent months, massive clean-up operations and environmental studies have begun on four of the most polluted waterways in the U.S. — all of them in the Tri-State area. Parts of the Passaic River, the Hudson River, the Gowanus Canal and Newtown Creek have all been deemed Superfund sites, meaning abandoned hazardous waste made them so highly toxic that the government required the parties responsible for polluting them to pay for their cleanup.

The process of cleaning a Superfund site is an economically, politically and physically arduous one. So in the wake of last week’s news about the dredging of the Hudson and Passaic, MetroFocus examined how the responsible parties plan to clean our waters.

This graphic shows the steps involved in the first phase of cleaning the lower Passaic River. Construction of the dredging enclosure began on Oct. 31. Image courtesy of the EPA.

The Passaic River, Northern New Jersey — from Garfield, N.J. to the mouth of the Newark Bay

When it became a Superfund site: 1984

What’s in the water: Polychlorinated biphenyls, commonly known as PCBs, are toxic organic compounds that adversely affect the nervous system of humans and animals. Once commonly used in manufacturing, PCBs take hundreds of years to break down in the environment. Also here: mercury; DDT and other pesticides; heavy metals; and most notably dioxin, the active chemical in Agent Orange.

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What’s happening now: Under an agreement between the Environmental Protection Agency and the two companies, Tierra and Occidental, a total of 200,000 cubic yards of polluted sediment will be dredged from the lower Passaic. The EPA and the Army Corps of Engineers will oversee the dredging. On Oct. 31, the EPA announced the start of construction on the first of two phases of dredging. Because of fears that dredging could stir up toxins and disperse them into the Atlantic Ocean, a construction team will first build a massive enclosure around the work site, then build a pipeline to transport the sediment downstream to the Upland Processing Facility in Newark, and finally bury the sediment in a landfill. The dredging will begin in March of 2012.

A map showing the Hudson River Superfund area. The second phase of cleanup began in June. Image courtesy of Mound of Sound.

The Hudson River — from Hudson Falls, N.Y. to Battery Park in Lower Manhattan

The EPA pulled this Atlantic Tomcod from the Hudson River. This fish, and others, were found to have developed mutant genes linked to pollution. Photo courtesy of termscience.com

In 2002, the EPA declared the Hudson River a Superfund site, and General Electric was charged with cleaning 40 miles of the river. In 2009, the EPA and General Electric spent six months dredging 10 sites on the river, processing the sediment and performing wildlife restoration as part of the first phase of the cleanup. As was the case with the Passaic, the dredging operation sparked fears among state environmental regulators about the possibility of PCBs surfacing into the water. In response, General Electric created an experimental system of wells and tunnels to shuttle sediment from the sediment caked at the bottom of the river to nearby processing facilities, without it entering the water.

Map showing the Newtown Creek Superfund site. The area in pink delineates the oil spill underneath Greenpoint, Brooklyn.The area is blue is zoned for residential use. Image courtesy of Riverkeeper.

Newtown Creek, from Greenpoint/Long Island City to Bushwick, Brooklyn

When it became a Superfund site: 2010

What’s in the water: Lots of oil resulting from a big oil spill; PCBs; raw sewage; pesticides; volatile organic compounds; heavy metals; and a chemical conglomerate known as “black mayonnaise” because of its texture.

In 1978, a helicopter discovered a large plume of oil in the creek. An investigation determined that historic refineries had leaked somewhere between 17 and 30 million gallons of oil underneath residential Greenpoint over the course of the past century. It was at the time the worst spill in North American history (the Deepwater Horizon disaster took that mantle in 2010). Much of that oil continues to seep into the creek. However, no action was taken until 1990, when New York State ordered Mobil Oil Corporation — a direct descendant of Standard Oil Company, which later became ExxonMobil — to perform what most environmental advocates said was a feeble attempt at a cleanup.

The view of Newtown Creek from the Pulaski Bridge, which separates Greenpoint, Brooklyn from Long Island City, Queens. Active industry, visible in the photo, sprawls along the banks of the creek. MetroFocus/Sam Lewis.

Pictured above are debris found on the banks of the Gowanus Canal. The EPA is currently conducting its second study of the Superfund site, but the agency says it may never be safe for swimming. Flickr/f.trainer

Since the canal is only open at one end, the water is basically stagnant, and only contains one-quarter of the oxygen required to support life. Nearby sewage overflows frequently flood the canal with raw human waste. In 1994, the New York City Department of Environmental Protection refurnished an old tidal pump to circulate water in the canal and reduce pollution, with lackluster results.